Chemotaxis in the cellular slime molds: I. The effect of temperature

Abstract

The effect of temperature on chemotaxis in the cellular slime mold Dictyostelium discoideum has been studied by incubating small populations of washed myxamoebae at different temperatures. Droplets containing a cell suspension of known density were deposited on a hydrophobic agar surface. The myxamoebae normally stayed within the boundaries of the implanted droplets, but they moved outside the margins of such droplets when they were attracted by acrasin secreted by neighboring populations. Sensitive cells in the responding populations were mainly attracted between the beginning of aggregation and its completion in the attracting populations. Secretion of acrasin before the formation of compact centers of aggregation was demonstrated at low temperatures and with time lapse photography. A decrease in temperature was correlated with: (1) an increase in the distance of attraction; (2) an increase in the time interval between the beginning of aggregation and its completion; and (3) an increase in the lapse of time between the deposition of the myxamoebae and the beginning of aggregation. The chronological age of the attracting cells did not seem to affect the chemotactic response. The increased attraction at lower temperatures was correlated with a longer period between early aggregation and its completion. Only the temperature during aggregation had an effect on the distance over which cells could be oriented; any temperature change applied during the preaggregative stages was of no consequence to the attraction at later stages.